Collum usually with 5+5 cones/spines in anterior row, 3+3 cones/spines in intermediate row and 4+4 cones/spines in posterior row. Similar in this respect to G. parvoterga sp. nov. Differs from this species by having paraterga longer; the degree of elevation of paraterga higher; male femora 5, 6 and 7 unmodified.

Gigaxytes gigas gen. et comb. nov. is presently known only from Krabi, Nakhon Si Thammarat, Phatthalung and Trang Provinces. Specimens were collected from limestone habitats and were mostly seen hiding under dead leaves, sometimes crawling on leaf litter. It has been found in syntopy with two species of other dragon millipedes at several locations across its distribution: Desmoxytes cervina and Desmoxytes delfae ( Jeekel, 1964). Notably, G. gigas gen. et comb. nov. was usually seen living and crawling on the ground whereas D. cervina and D. delfae were collected from rocks and tree branches.

Based on extensive fieldwork focused on this genus in southern Thailand, G. gigas gen. et comb. nov. is one of the most common and widely distributed dragon millipedes in many provinces. It is sometimes encountered close to the areas that have been developed as tourist attractions such as caves, as well as a temple or bureau of monks. However, it is still found in natural habitats and has a rather limited distribution in southern Thailand; we here regard this species as endemic for the Thai fauna.

Note on material

‘ Desmoxytes ’ gigas Golovatch & Enghoff, 1994 was described on the basis of a single adult female (in ZMUC) collected from Krabi Province. We have collected additional specimens in many areas, males as well as females. After examination of all material, it is clear that morphological characters of adult females collected from Krabi, Nakhon Si Thammarat, Phatthalung and Trang Provinces match perfectly with the female holotype.

Remarks

The living colouration of adults is generally pinkish brown that blends perfectly with brown/pinkish brown leaves or litter on the ground; juveniles are brown.

Two main populations, eastern and western, can be distinguished on the basis of morphological differences in combination with distribution. The two populations differ in characters of paranota and gonopod femorite: specimens of the western population have obviously longer paraterga and the femorite more slender than those of the eastern one. Intrapopulational variation also exists: epiproct with conspicuous apical setiferous tubercles in some specimens, inconspicuous in others; hypoproct subtrapeziform in some specimens, subrectangular in others.

Some specimens of G. gigas gen. et comb. nov. were infested with parasitic mite larvae, probably belonging to the genus Leptus Latreille, 1896. Several mites appeared on metaterga in anteriormost rings and could easily be discerned ( Fig. 9B, CView Fig. 9) by their remarkable orange colour. Mite larve assigned to the genus Leptus were reported from a few dragon millipede species (genera Desmoxytes and Nagaxytes) by Srisonchai et al. (2018a, b). We suspect that all? Leptus larvae from dragon millipedes might belong to the same species. However, an exact identification of the mite species has not been undertaken, and in any case, the relationship between the millipede and Leptus still requires further studies.

As mentioned in the diagnosis, the new species is noticeably different from other Gigaxytes species due to its unmodified male femora 5–7.